Fuse holder



June 1962 R. P. ARTHUR ETAL 3,038,977

FUSE HOLDER Filed April 4, 1961 INVENTOR ate r are ea- 3,038,977 FUSEHOLDER Richard P. Arthur, Hinsdale, and Neris J. Simkus, Willow Springs,111., assignors to international Telephone and Telegraph Corporation,New York, N.Y., a corporation of Maryland Filed Apr. 4, 1961, Ser. No.169,625 8 Claims. (Cl. 200-433) This invention relates to fuse holdersand more particularly to holders for grasshopper fuses.

In the electrical arts, wires or bars of fusing material having a lowmelting point and suspended between two electrodes through which currentflows. If the current exceeds a predetermined amount, this fuse wire orbar melts and opens an electrical circuit, thus terminating the currentand removing an applied potential to protect delicate electricalequipment from damage by overload conditions. Usually, a burnedout fuseis immediately apparent because the electrical equipment controlledthereby ceases to function. However, in some equipment it is necessaryto provide means for signaling a burned-out fuse alarm because theequipment is not under observation and, therefore, a burned-out fuse isnot immediately apparent.

One of the best known devices for signaling a burnedout fuse alarm isthe so-called grasshopper fuse wherein the fuse wire or bar holds a leafspring contact in a retracted position against its spring tension. Whenthe fuse burns out, the wire or bar melts, the spring tension isreleased, and the leaf spring moves from its retracted to its normalposition where an electrical circuit is completed to an alarm device.While the grasshopper fuse and all of its associated circuitry has beenused for an extremely long period of time, virtually no improvementshave been made in devices for holding them. A result is that thegrasshopper fuse holder in current use is, relatively speaking, one ofthe most expensive components used in telephone switching and otherelectrical equipment.

Accordingly, an object of this invention is to provide a new andimproved fuse holder. More particularly, an object is to provide lowcost fuse holders for grasshopper type fuses. Another object of thisinvention is to provide a low cost fuse holder made by a minimum numberof inexpensive, general purpose tools.

In accordance with one aspect of this invention, a fuse holder isfashioned from a unitary bracket of electrical insulating materialhaving a number of cavities formed therein. Each cavity is shaped toreceive and support a grasshopper fuse, the orientation of the cavitiesbeing such that a number of grasshopper fuses are supported in spacedparallel relation. A pair of electrical contact terminals are positionedin each cavity to provide an electrical circuit through which currentflows, and a third electrical contact terminal is positioned in thecentral part of the cavity to provide a path to an alarm device. In thismanner, the electrical current may be directed through the fuse wirewhich supports the leaf spring and if a fuse burns out the leaf springmakes contact with the third terminal to signal an alarm.

The above mentioned and other features and objects of this invention andthe manner of obtaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a perspective View of a grasshopper fuse;

FIG. 2 is a front elevation view showing a fuse holding bracket with onegood and one burned-out grasshopper fuse;

FIG. 3 is a side elevation view of the bracket of FIG. 1

with a portion broken away to show the manner of inserting electricalcontact terminals;

FIG. 4 is an enlarged view of a single fuse holding cavity showing thedetails thereof;

PEG. 5 is a sectional view of the cavity taken along line 55 of FIG. 4;and

FIG. 6 is a perspective view of the cavity portion shown in 4.

While the principles of a grasshopper fuse are well known, it may behelpful to review them briefly by referring to FIG. 1 which shows ageneral configuration of such a fuse. It includes an elongated fiat bar20 of electrical insulating material which may be stamped out of a sheetof phenolic resin material, for example. As shown in this figure, theright-hand end of the plate 2i) includes a longitudinally extending slot21 and the lefthand end includes a transversely extending slot 22.Surrounding these slots are terminals 23, 24 of electrically conductivematerial, which may be sheet metal folded over the end of bar 21') andcrimp fastened thereto. A downwardly extending leaf spring member 26 issecured between the bar 20 and the end terminal 24. On the opposite endand side of the bar 20 and somewhat secured between the bar and endterminal 23 is an upwardly extending boom portion 27. The fuse wire 28is attached in any suitable manner (for example, it may be soldered intoposition) between the upper boom 27 and the lower leaf spring 26. Thelength of the fuse wire 28 is such that the leaf spring 26 is raisedagainst its spring tension to a retracted position. When the fuse wireburns out, the lower leaf spring moves under its own spring tension toits normal untensioned position where an alarm condition is indicated.

In accordance with one aspect of this invention, a grasshopper fuseholder includes a unitary bracket 30 made of any good electricalinsulating material, such as Bakelite, for example. The bracket isfashioned in any suitable manner (as by molding, for example) into agenerally rectangular shape with a series of elongated cavities 31formed one above the other to provide means for receiving and supportinga number of grasshopper fuses in spaced parallel relation, two of whichare shown at 32, 33. As shown in the drawing, there is space in thebracket for receiving and supporting five grasshopper fuses. A dottedline 34 indicates the outer contour of the cavities that would be seenif the bracket 30 were viewed from the back.

Each cavity includes an enlarged central portion a having a pair ofcommunicating, reduced portions 12, b extending therefrom inlongitudinally aligned and diametrically opposed relation. The depth 1of each cavity is approximately the same as the transverse dimension 2of a grasshopper fuse. Therefore, the overall configuration anddimensions of the cavity including the enlarged central and reduced endportions correspond generally to the overall configuration anddimensions of a grasshopper fuse. Thus, as shown at 32, 33 in FiG. 1, agrasshopper fuse may be inserted sideways into and removed from each ofthe cavities.

To provide electrical connections between each fuse and associatedequipment, a number of electrical contact terminals 35-37 are positionedin each cavity. These contacts may be inserted either into the mold atthe time of casting or, at a later time, into openings formed in thebracket. First and second terminals 35, 36 are positioned in each of thereduced portions b, b to make electrical contact between a battery B anda Load via the end terminals 24, 23 of the grasshopper fuse. The thirdcontact terminal 37 is placed in the central portion immediately beneaththe leaf spring 26 of a grasshopper fuse when it is inserted into thefuse holder; however, unless the fuse is burned-out, the verticaldistance d between the leaf spring and the third electrical contact 37is such that the spring does not touch the third contact. If the fusedoes burn out, the leaf spring 26 moves under its own spring tension andmakes contact with the third electrical contact 37. This completes acircuit for signaling an alarm to indicate the burned-out fusecondition. To illustrate this operation a burned-out fuse is shown at 33where the leaf spring 26 is touching the contact 37'.

To polarize the physical positioning of the grasshopper fuse when it isinserted into the cavity, a boss 40 is formed in one of the recessedopenings. As shown in FIG. 1, conventional grasshopper fuses normallyhave a longitudinally extending slot 21 adjacent one end and atransversely extending slot 22 adjacent the other end. In prior fuseholders the practice has been to provide two bolts or screws, a first ofwhich is loosened to receive the slot 21 which is slipped under thescrew head. Then the fuse is rotated in the direction of the arrow (R)so that the transversely extending slot 22 fits beneath the other screwhead. Thereafter both screws are tightened. Since the inventioncontemplates using the same type grasshopper fuse, the boss 40 isadvantageously positioned so that only the transversely extending slot22 may be fitted into reduced portion b of the cavity. In this manner itis impossible to insert the grasshopper fuse in any position except thecorrect one.

To facilitate gripping the grasshopper fuse while it is being insertedinto or removed from the cavity, an edge portion of the cavity isrecessed, as shown at 41. Preferably, this recessed portion ispositioned near terminal 35 (assuming an electrical connection as shownin FIG. 4) so that any electrically conductive portion of thegrasshopper fuse which may be touched while a burned-out fuse is beingremoved is at ground potential. Therefore, if one uses his fingers toremove a fuse, the danger of shock is substantially reduced. Also, therecessed por tion 41 allows insertion of the jaws of pliers, if they areused to remove the fuse. There is no substantial hazard while the fuseis being inserted because the pushing action eliminates contact with theconductive materials.

An advantage of this invention is that the fuse holder requires only onetool of special design and that is the mold in which the bracket iscast. Once the mold is purchased, the brackets can be mass produced fora few cents. In one specific instance, the International Telephone andTelegraph Corporation found that it had a cost savings of approximately80% to 85% when it adopted the design shown and described herein. Moreover, the fuse holder is entirely compatible with existing equipment anddoes not require scrapping existing parts or replacing non-worn-outparts. Finally, the overall dimensions of the fuse holder are the sameas the dimensions of commonly used fuse holders so that they may bereplaced quickly and easily. However, when new equipment is designed,the dimensions of fuse holders made according to the teachings of thisinvention may be reduced to allow some degree of miniaturization.

It is to be understood that the foregoing description of a specificexample of the invention is not to be considered as a limitation on itsscope.

We claim:

1. A holder for grasshopper fuses comprising a bracket of electricalinsulating material having elongated cavities formed therein, a centralportion of each cavity being enlarged to receive the central portion ofa grasshopper filse and the elongated dimension of each cavity beingshaped to receive end terminals of a grasshopper fuse, the depth of eachcavity being approximately the same as the transverse dimension of agrasshopper fuse, whereby a fuse is received in and supported by each ofthe cavities, three electrical contact terminals in each cavity, firstand second of said contact terminals being placed in the ends of saidcavity to make electrical contact with said fuse when inserted into saidcavity, and the third of said contact terminals being placed in saidcentral opening to make contact with said grasshopper fuse when saidfuse is burned-out.

2. A holder for grasshopper fuses comprising a unitary bracket ofelectrical insulating materials having a number of spaced parallelelongated cavities formed therein, each cavity being shaped to receiveand support a grasshopper fuse when inserted into said cavity, meansincluding a recessed portion formed on one edge of each of said cavitiesto facilitate removal of a grasshopper fuse from said cavity, threeelectrical contact terminals positioned in each of said cavities, firstand second of said three contact terminals being placed in the ends ofsaid elongated cavity to make electrical contact with a fuse when saidfuse is inserted into said cavity, and the third of said contactterminals being placed in a central portion of said cavity to makecontact with a leaf spring on said grasshopper fuse when said fuse isburned-out.

3. The fuse hold-er of claim 2 wherein said recessed portion ispositioned near the ground side of said fuse.

4. A holder for grasshopper fuses comprising a unitary molded bracket ofelectrical insulating material having a number of vertically alignedcavities formed therein, each cavity comprising an enlarged centralportion having a pair of communicating reduced portions extendingtherefrom in longitudinally aligned and diametrically opposed relation,said central portion being shaped to re ceive the central portion of agrasshopper fuse and each of said reduced portions being shaped toreceive a corresponding end terminal of said grasshopper fuse when saidgrasshopper fuse is inserted into said cavity, means including arecessed portion formed on one edge of each of said cavities tofacilitate gripping said grasshopper fuse while it is removed from saidcavity, three electrical contact terminals positioned in each of saidcavities, first and second of said three contact terminals being placedin the ends of said cavity to make electrical contact with terminals onthe ends of said fuse when inserted into said cavity, the third of saidcontact terminals being placed in said central position to make contactwith a leaf spring on said grasshopper fuse when said fuse isburned-out, and means for applying ground and battery potentials acrosssaid first and second contact terminals, said recessed portion beingpositioned adjacent to said ground terminal thereby reducing the dangerof electrical shock while said fuse is being removed from said opening.

5. A holder for grasshopper fuses comprising a unitary bracket ofinsulating material having a number of elon gated cavities formedtherein, each cavity being shaped to receive and support a grasshopperfuse when inserted sideways into said cavity, means comprising a bossformed in one end of each of said cavities for polarizing the physicalposition of said grasshopper fuse when it is inserted into said cavity,three electrical contact terminals positioned in each of said cavities,first and second of said three contact terminals being placed inopposite ends of said cavity to make electrical contact with each end ofa fuse when said fuse is inserted into said cavity, and the third ofsaid contact terminals being placed in a central portion of said cavityto make contact with leaf spring on said grasshopper fuse when said fuseis burned-out.

6. The fuse holder of claim 5 wherein said boss is positioned to exposethe grounded side of the fuse to reduce the hazard of shock.

7. A holder for grasshopper fuses comprising a unitary bracket ofinsulating material having at least one cavity formed therein, saidcavity comprising an enlarged central portion having a pair ofcommunicating reduced portions extending therefrom in longitudinallyaligned and diametrically opposed relation, said central portion beingshaped to receive the central portion of a grasshopper fuse and each ofsaid reduced portions being shaped to receive a corresponding endterminal of said grasshopper fuse when said fuse is inserted into saidcavity, means comprising a boss formed in at least one of said reducedportions for polarizing the physical position of said grasshopper fusewhen inserted into said cavity, means including a recessed portionformed on one edge of said cavity to facilitate removal of saidgrasshopper fuse from said cavity, three electrical contact terminals insaid cavity, first and second of said three contact terminals beingplaced in opposite ends of said cavity to make electrical contact withsaid end terminals on said fuse When said fuse is inserted into saidcavity, and the third of said contact terminals being placed in saidcentral portion to make contact with a leaf spring on said grasshopperfuse when said fuse is burned-out.

8. A grasshopper fuse holder comprising a bracket of insulating materialhaving at least one cavity formed therein, said cavity comprising anenlarged central portion having a pair of communicating reduced portionsextending therefrom in longitudinally aligned and diametrically opposedrelation, said central portion being shaped to receive the centralportion of a grasshopper fuse and each of said reduced portions beingshaped to receive a corresponding end terminal of said grasshopper fusewhen said grasshopper fuse is inserted into said cavity, meanscomprising a boss formed in at least one of said reduced portions forpolarizing the physical position of said grasshopper fuse when it isinserted into said cavity, means including a recessed portion formed insaid cavity to facilitate removal of said grasshopper fuse from saidcavity, three electrical contact terminals in said cavity, first andsecond of said three contact terminals being placed in the ends of saidcavity to mate with said fuse terminals when said fuse is inserted intosaid cavity, means for applying ground and battery potentials across thecontact terminals placed in the ends of said cavities, said recessedportion being positioned adjacent to said ground terminal, and the thirdof said contacts being placed in said central opening to make contactwith a leaf spring on said grasshopper fuse when said fuse isburned-out.

References Cited in the file of this patent UNITED STATES PATENTS761,916 Rorty et al June 7, 1904 819,608 Sherwood May 1, 1906 2,923,796Davis Feb. 2, 1960

